ML20066D934
| ML20066D934 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 01/10/1991 |
| From: | Beck G PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9101170144 | |
| Download: ML20066D934 (3) | |
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i PHILADELPHIA ELECTRIC COMPANY NUCLEAR GROUP HEADQUARTERS 955 65 CHESTERBROOK BLVD.
l WAYNE, PA 19087 5691 j
(ri s) sao.soco January 10, 1991 Docket Nos.
50-352 50-353 License Nos. NPF-39 i
NPF-85 i
U.S. Nuclear Regulatory Commission ATTH: Document Control Desk Washington, D.C.
20555 i
SUBJECT:
Limerick Generating Station. Units 1 and 2 Philadelphia Electric Company Position on Operability of the Main Control Room fleating, Ventilation, and Alr-Conditioning System Chlorine Isolation Mode Gentlemen On February 26, 1990 PhiladelphiaElectricCompany(PECo) submitted LicenseeEventReport(LER)-No. 1-90-002 "The Main Control Room Ventilation System is outside of the design basis due to misapplication of the design basis assumptions," for Limerick Generating Station (LGS), Units 1 and 2.
This LER reported that, as a result of a modification, the chlorine detection system for the automatic chlorine isolation mode of the Main Control Room (MCR) Heating.
Ventilation, and Air Conditioning (HVAC) system no longer meets the single failure criterion when the MCR HVAC system is in the radiation isolation mode.
A meeting was subsequently held on March 7,1990, between representatives of PECo and the NRC to further discuss the details of this condition, including the operability of the chlorine detection system in accordance with Technical Specifications (TS). At this meeting, PECo representatives provided the NRC with the results of a HCR habitability analysis with regard to the NCR HVAC system remaining in the radiation isolation mode in the event of a chlorine release accident affecting the LGS site. The information below provides a-synopsis of the condition, the results_of the habitability analysis, and PECo's position on the operability of the NCR chlorine detection system.
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Document Control Desk January 10, 1991 Page ?
if chlorine is introduced after the MCR llVAC system is already in the radiation isolation mode i.e., with the outside air intake dampers open),
because of testing or as r(equired by the Action statement of the associated TS Limiting Condition of Operation (LCO), the chlorine detectors would tense the presence of chlorine and initiate an automatic isolation of the MCR outside air intake dampers, thus overriding the radiation isolation mode, llowever, the logic of the chlorine detection system with the MCR llVAC system initially in the radiation isolation mode is such that a single failure of the chlorine detection system could allow the filtered outsile air intake dampers to remain open, and thus, the MCR llVAC system would remain in the radiation isolation mode.
Under these circumstances, once the chlorint has been detected and alarwed in the NCR, manual action can be taken to reallgr the system to the chlorine isolation mode.
Analysis of this event assuh.es that the MCR llVAC system remains in the radiation isolation mode with 525 cfm of outside air being mixed with 2.475 cfm of recirculated MCR air for a total of 3,000 cfm being passed through the charcoal adsorber filter trains, and that the filter has no effect on removal of chlorine. The results of the analysis indicate that, with the MCR IfVAC system in the radiation isolation mode, automatic chlorine isolation is not required to satisfy General Derign Criterton (GDC) 19 of 10 CfR 50. Appendix A.
Calculations show that the incapacitation time due to a railroad release of chlorine gas with the MCR llVAC system operating in the radiation isolation mode, with an elevated air intake, is 6.5 minutes.
This time is greater than the 4.3 minute incapacitation time given in the Updated final Safety Analysis Report (UfSAR) for a rallroad release of chlorine with the MCR llVAC system operating in the chlorine isolation mode with ground level air intake. While in the radiation isolation mode, the only source of chlorine is through the elevated air intake.
Regulatory Guide 1.78, " Assumptions for Evaluating the liabitability of a Nuclear Power Plant Control Room During a Postulated llazardous Chemical Release " Revision 0, has a two minute guideline for incapacitation times.
Thus, the MCR operators would have sufficient time to don breathing apparatus after an alarm has sounded in the MCR. Since automatic chlorine isolation is not required to satisfy G0C 19 under this condition, the chlorine detection system is considered operable in accordance with the associated TS LC0 when the MCR llVAC system is in the radiation isolation mode, even though the logic of the chlorine detection system for automatic chlorine isolation is not " single failure proof" in this condition.
Additionally, LER 1-90-002 reported a condition whereby automatic entry into the radiation isolation mode of the MCR llVAC system will not occur upon receipt of a high radiation signal when the NCR llVAC system is initially in the chlorine isolation mode. This original system design recognizes that the inflitration of chlorine gas into the NCR is a more imediate threat to the operations personnel in the event of an accident resulting in both high radiation exposure and chlorine gas exposure. The information below describes the results of the NCR habitability analysis provided to the NRC at the March 7, 1990 meeting with regard to the MCR llVAC system remaining in the chlorine isolation mode in the event of a postulated radioactive release accident.
Document Centrol Desk January 10, 1991 Page 3
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Calculations show the MCR operator radiation exposure doses with the MCR HVAC system operating in the chlorine isolation mode are well below the GDC 19 limits.
The following table compares calculated personnel doses for the NCR llVAC system operating in the radiation isolation mode and the chlorine isolation mode during a UFSAR postulated radiation accident.
Radiation Chlorine GDC 19 Isolation Mode (res)
IsolationMode(real Limits (res)
Thyroid 0.0043 14.0 30 Skin Beta 7.6 7.6 30 Whole-Body Gamma 0.38 0.38 5
The chlorine isolation mode personnel doses are based on methodology given in NUREG-0991, "Saftdy Evaluation Report Related to the Operation of Limerick Generating Station, Units 1 and 2."
As a result of the increased thyroid dose while in the chlorine isolation mode, PECo is considering a future change to the chlorine detection system TS Action statements regarding actions to be taken when the system is out of service. This was discussed with the NRC at the March 7, 1990 meeting.
Based on the results of the MCR habitability analysis under both conditions, we have concluded that the MCR continues to satisfy GDC 19 and the MCR operators are sufficiently protected from both chlorine and radiological accidents when the MCR HVAC system is in either the chlorine or radiation isolation mode.
If you have any questions, please do not hesitate to contact us.
Very truly yours,
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G. [ Beck Manager Licensing Section Nuclear Engineering and Services GilS:c1p cc:
T.1. Martin, Administrator, Region I USNRC T. J. Kenny, USNRC Senior Resident inspector, LCS 1
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